Mathematical Model of Airflow in the Lungs of Children I: Effects of Tumor Sizes and Locations

Deciphering Exhaled Aerosol Fingerprints for Early Diagnosis and Personalized Therapeutics of Obstructive Respiratory Diseases in Small Airways

Respiratory diseases often show no apparent symptoms at their early stages and are usually diagnosed when permanent damages have been made to the lungs. A major site of lung pathogenesis is the small airways, which make it highly challenging to detect using current techniques due to the diseases’ location (inaccessibility to biopsy) and size (below normal CT/MRI resolution). In this review, we present a new method for lung disease detection and treatment in small airways based on exhaled aerosols, whose patterns are uniquely related to the health of the lungs. Proof-of-concept studies are first presented in idealized lung geometries. We subsequently describe the recent developments in feature extraction and classification of the exhaled aerosol images to establish the relationship between the images and the underlying airway remodeling. Different feature extraction algorithms (aerosol density, fractal dimension, principal mode analysis, and dynamic mode decomposition) and machine learning approaches (support vector machine, random forest, and convolutional neural network) are elaborated upon. Finally, future studies and frequent questions related to clinical applications of the proposed aerosol breath testing are discussed from the authors’ perspective. The proposed breath testing has clinical advantages over conventional approaches, such as easy-to-perform, non-invasive, providing real-time feedback, and is promising in detecting symptomless lung diseases at early stages.

Pediatric in vitro and in silico models of deposition via oral and nasal inhalation

Respiratory tract deposition models provide a useful method for optimizing the design and administration of inhaled pharmaceutical aerosols, and can be useful for estimating exposure risks to inhaled particulate matter. As aerosol must first pass through the extrathoracic region prior to reaching the lungs, deposition in this region plays an important role in both cases. Compared to adults, much less extrathoracic deposition data are available with pediatric subjects. Recently, progress in magnetic resonance imaging and computed tomography scans to develop pediatric extrathoracic airway replicas has facilitated addressing this issue. Indeed, the use of realistic replicas for benchtop inhaler testing is now relatively common during the development and in vitro evaluation of pediatric respiratory drug delivery devices. Recently, in vitro empirical modeling studies using a moderate number of these realistic replicas have related airway geometry, particle size, fluid properties, and flow rate to extrathoracic deposition. Idealized geometries provide a standardized platform for inhaler testing and exposure risk assessment and have been designed to mimic average in vitro deposition in infants and children by replicating representative average geometrical dimensions. In silico mathematical models have used morphometric data and aerosol physics to illustrate the relative importance of different deposition mechanisms on respiratory tract deposition. Computational fluid dynamics simulations allow for the quantification of local deposition patterns and an in-depth examination of aerosol behavior in the respiratory tract. Recent studies have used both in vitro and in silico deposition measurements in realistic pediatric airway geometries to some success. This article reviews the current understanding of pediatric in vitro and in silico deposition modeling via oral and nasal inhalation.

Exhaled aerosol pattern discloses lung structural abnormality: a sensitivity study using computational modeling and fractal analysis

BACKGROUND

Exhaled aerosol patterns, also called aerosol fingerprints, provide clues to the health of the lung and can be used to detect disease-modified airway structures. The key is how to decode the exhaled aerosol fingerprints and retrieve the lung structural information for a non-invasive identification of respiratory diseases.

OBJECTIVE AND METHODS

In this study, a CFD-fractal analysis method was developed to quantify exhaled aerosol fingerprints and applied it to one benign and three malign conditions: a tracheal carina tumor, a bronchial tumor, and asthma. Respirations of tracer aerosols of 1 µm at a flow rate of 30 L/min were simulated, with exhaled distributions recorded at the mouth. Large eddy simulations and a Lagrangian tracking approach were used to simulate respiratory airflows and aerosol dynamics. Aerosol morphometric measures such as concentration disparity, spatial distributions, and fractal analysis were applied to distinguish various exhaled aerosol patterns.

FINDINGS

Utilizing physiology-based modeling, we demonstrated substantial differences in exhaled aerosol distributions among normal and pathological airways, which were suggestive of the disease location and extent. With fractal analysis, we also demonstrated that exhaled aerosol patterns exhibited fractal behavior in both the entire image and selected regions of interest. Each exhaled aerosol fingerprint exhibited distinct pattern parameters such as spatial probability, fractal dimension, lacunarity, and multifractal spectrum. Furthermore, a correlation of the diseased location and exhaled aerosol spatial distribution was established for asthma.

CONCLUSION

Aerosol-fingerprint-based breath tests disclose clues about the site and severity of lung diseases and appear to be sensitive enough to be a practical tool for diagnosis and prognosis of respiratory diseases with structural abnormalities.

Delivery of inhalation drugs to children for asthma and other respiratory diseases

Infants and children constitute a patient group that has unique requirements in pulmonary drug delivery. Since their lungs develop continuously until they reach adulthood, the airways undergo changes in dimensions and number. Computational models have been devised on the growth dynamics of the airways during childhood, as well as the particle deposition mechanisms in these growing lungs. The models indicate that total aerosol deposition in the body decreases with age, while deposition in the lungs increases with age. This has been observed on paediatric subjects in in vivo studies. Issues unique to children in pulmonary drug delivery include their lower tidal volume, highly variable breathing patterns, air leaks from facemasks, and the off-label or unlicensed use of pharmaceutical products due to lack of clinical data for this age group. The aerosol devices used are essentially those developed for adult patients that have been adapted to paediatric use. Facemasks should be used with nebulisers and spacers for infants and young children. An idealised throat that mimic the average particle deposition in paediatric throats has been designed to obtain more clinically relevant aerosol dispersion data in vitro. More effort should be spent on studying particle deposition in the paediatric lung and developing products specific for this subpopulation to meet their needs.

In silico modeling of asthma

The incidence of asthma is increasing throughout the world, especially among children, to the extent that it has become a medical issue of serious global concern. Appropriately, numerous pharmacologic drugs and clinical protocols for the treatment and prophylaxis of the disease have been reported. From a scientific perspective, a review of the literature suggests that the targeted delivery of an aerosol would, in a real sense, enhance the efficacy of an inhaled medicine. Therefore, in accordance with published data we have developed a mathematical description of disease-induced effects of disease on airway morphology. A morphological algorithm defining the heterogeneity of asthma has been integrated with a computer code that formulates the behavior and fate of inhaled drugs. In this work, predicted drug particle deposition patterns have been compared with SPECT images from experiments with healthy human subjects (controls) and asthmatic patients. The asthma drug delivery model simulations agree with observations from human testing. The results indicate that in silico modeling provides a technical foundation for addressing effects of disease on the administration of aerosolized drugs, and suggest that modeling should be used in a complementary manner with future inhalation therapy protocols.

Targeted drug aerosol deposition analysis for a four-generation lung airway model with hemispherical tumors

One important research area of broad interest is the development of highly efficient drug delivery systems for desired site deposition and uptake. For example, controlled drug aerosol release and targeting to specific regions of the lung is a novel way to combat lung diseases, diabetes, virus infections, cancers, etc. Determination of feasible air-particle streams is a prerequisite for the development of such delivery devices, say, smart inhalers. The concept of "controlled particle release and targeting" is introduced and results are discussed for a representative model of bronchial lung airways afflicted with hemispherical tumors of different sizes and locations. It is shown that under normal particle inlet conditions a particle mass fraction of only up to 11% may deposit on the surface of a specific tumor with critical radius r/R approximately 1.25, while a controlled particle release achieves deposition fractions of 35 to 92% for a realistic combination of inlet Stokes and Reynolds numbers, depending mainly on tumor size. Furthermore, with the controlled release and targeting approach nearby healthy tissue is hardly impacted by the typically aggressive drug aerosols. Assuming laminar, quasi-steady, three-dimensional air flow and spherical non-interacting micron-particles in sequentially bifurcating rigid airways, the results were obtained using a validated commercial finite-volume code with user-enhanced programs on a high-end engineering workstation. The new concept is generic and hence should be applicable to other regions of the respiratory system as well.

Risk assessment dosimetry model for inhaled particulate matter: II. Laboratory surrogates (rat)

Inhalation toxicology investigations are often performed with laboratory animals to address the potential health effects of inhaled air pollutants on human beings. In Part II of this risk assessment study we have considered the deposition of inhaled particulate matter in the laboratory rat as the surrogate of choice. Calculations were performed in an analogous manner to those conducted in Part I for human subjects. To simulate a wide range of human respiratory intensities associated with different levels of physical activities that must be recognized in the determination of air pollution standards, the CO(2) concentrations within animal inhalation exposure chambers may be controlled. Accordingly, we have regulated rat breathing parameters to correspond to a range of human activities, from rest to work. The results of this interspecies modeling study have been presented in a variety of graphical formats to ease comparisons with findings from experiments and to facilitate integration of the results into risk assessment analyses. The findings of our work clearly demonstrate that interspecies simulations can be employed to design animal tests a priori so that the results can be effectively and efficiently extrapolated to human conditions in a meaningful manner.